Method and apparatus for enhancing channel strain

ABSTRACT

An apparatus includes a substrate having a strained channel region, a dielectric layer over the channel region, first and second conductive layers over the dielectric layer having a characteristic with a first value, and a strain-inducing conductive layer between the conductive layers having the characteristic with a second value different from the first value. A different aspect involves an apparatus that includes a substrate, first and second projections extending from the substrate, the first projection having a tensile-strained first channel region and the second projection having a compression-strained second channel region, and first and second gate structures engaging the first and second projections, respectively. The first gate structure includes a dielectric layer, first and second conductive layers over the dielectric layer, and a strain-inducing conductive layer between the conductive layers. The second gate structure includes a high-k dielectric layer adjacent the second channel region, and a metal layer.

BACKGROUND

As the semiconductor industry has strived for higher device density,higher performance, and lower costs, problems involving both fabricationand design have been encountered. One solution to these problems hasbeen the development of a fin-like field effect transistor (FinFET). Atypical FinFET includes a thin vertical ‘fin’ formed by etching spacedrecesses into a substrate. The source, drain, and channel regions aredefined within this fin. The transistor's gate is wrapped around thechannel region of the fin, engaging it on both the top of the fin andthe sides of the fin. This configuration allows the gate to inducecurrent flow in the channel from three sides. Thus, FinFET devices havethe benefit of higher current flow and reduced short channel effects.

The dimensions of FinFETs and other metal oxide semiconductor fieldeffect transistors (MOSFETs) have been progressively reduced astechnological advances have been made in integrated circuit materials.However, this scaling-down trend has slowed due to physical limits of ICmaterials. Thus, other techniques to increase device performance havebeen devised. One such technique involves straining the channel regionof MOSFET devices to improve electron and hole mobility. Results hasbeen generally adequate, but the level of channel strain obtained thusfar has been not entirely satisfactory.

Additionally, there has been a trend in the semiconductor industry toreplace the traditional gate oxide and polysilicon gate electrode inFinFET devices with a high-k gate dielectric and metal gate electrode toimprove device performance. For example, replacement gate techniqueshave been devised to fabricate CMOS devices with dual metal gate FinFETdevices. However, high costs and burdensome complexity in thefabrication process have rendered dual metal gate devices less thanentirely satisfactory.

SUMMARY

According to one of the broader forms of the invention, an apparatusincludes a substrate having a strained channel region therein, adielectric layer disposed at least partly over the channel region, afirst conductive layer disposed over the dielectric layer, and having acharacteristic with a first value, a strain-inducing conductive layerdisposed over the first conductive layer, and having the characteristicwith a second value, wherein the second value is different from thefirst value, and a second conductive layer disposed over thestrain-inducing conductive layer, and having the characteristic with thefirst value.

According to another of the broader forms of the invention, an apparatusincludes a substrate, first and second projections extending upwardlyfrom the substrate, the first projection having a tensile-strained firstchannel region therein and the second projection having acompression-strained second channel region therein, and first and secondgate structures engaging the first and second projections adjacent tothe first and second channel regions, respectively. The first gatestructure includes a dielectric layer adjacent the first channel region,a first conductive layer disposed over the dielectric layer, astrain-inducing conductive layer disposed over the first conductivelayer, and a second conductive layer disposed over the strain-inducingconductive layer. The second gate structure includes a high-k dielectriclayer adjacent the second channel region, and a metal layer disposedover the high-k dielectric layer.

According to yet another of the broader forms of the invention, a methodincludes providing a substrate, forming a projection extending upwardlyfrom the substrate, the projection having a channel region therein,forming a gate structure engaging the projection adjacent to the channelregion, the gate structure having spaced first and second conductivelayers and a strain-inducing conductive layer disposed between the firstand second conductive layers, forming a capping layer over the gatestructure, imparting strain to the channel region, including performinga heat treatment on the gate structure, and removing the capping layer.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isemphasized that, in accordance with the standard practice in theindustry, various features are not drawn to scale. In fact, thedimensions of the various features may be arbitrarily increased orreduced for clarity of discussion.

FIG. 1 is a diagrammatic fragmentary perspective view of a CMOSsemiconductor device.

FIG. 2 is a diagrammatic fragmentary sectional view of the semiconductordevice taken along line 2-2 in FIG. 1.

FIG. 3 is a diagrammatic fragmentary sectional view of the semiconductordevice taken along line 3-3 in FIG. 1.

FIG. 4 is a diagrammatic fragmentary sectional view of the semiconductordevice taken along line 4-4 in FIG. 1.

FIGS. 5-12 are diagrammatic fragmentary sectional views similar to FIG.4 but showing the semiconductor device during various successive stagesof manufacture.

FIG. 13 is a high-level flowchart showing a process that is described inassociation with FIGS. 5-12.

DETAILED DESCRIPTION

The present disclosure relates generally to semiconductor devices andmore particularly, to a FinFET device and method of fabricating a FinFETdevice or portion of a device. It is understood, however, that specificembodiments are provided as examples to teach the broader inventiveconcept, and one of ordinary skill in the art can easily apply theteaching of the present disclosure to other methods or apparatus. Inaddition, it is understood that the methods and apparatus discussed inthe present disclosure include some conventional structures and/orprocesses. Since these structures and processes are well known in theart, they will only be discussed in a general level of detail.Furthermore, reference numbers are repeated throughout the drawings forsake of convenience and example, and such repetition does not indicateany required combination of features or steps throughout the drawings.Moreover, the formation of a first feature over and on a second featurein the description that follows may include embodiments in which thefirst and second features are formed in direct contact, and may alsoinclude embodiments in which additional features may be formedinterposing the first and second features, such that the first andsecond features may not be in direct contact.

FIG. 1 is a diagrammatic fragmentary perspective view of a CMOSsemiconductor device 10. The semiconductor device 10 is an integratedcircuit that includes a fin-like n-channel metal-oxide-semiconductorfield effect transistor (NMOS FinFET) 11 and a fin-like p-channelmetal-oxide-semiconductor field effect transistor (PMOS FinFET) 12. NMOSFinFET 11 and PMOS FinFET 12 may alternatively be any type of fin-basedtransistor. The FinFETs 11 and 12 may be part of a microprocessor,memory cell (e.g., SRAM), and/or other integrated circuits.

The NMOS FinFET 11 and PMOS FinFET 12 are formed on siliconsemiconductor substrate 13. The substrate 13 may alternatively includeother elementary semiconductors such as germanium, or include a compoundsemiconductor such as silicon carbide, gallium arsenide, indiumarsenide, and indium phosphide. Alternatively, the substrate 13 may be asilicon-on-insulator (SOI) substrate. In such a case, the SOI substratemay be fabricated using separation by implantation of oxygen (SIMOX),wafer bonding, and/or other suitable methods.

The semiconductor device 10 includes fin structures (or projections) 14and 16 that extend upwardly from the substrate 13 and form portions ofthe NMOS FinFET 11 and PMOS FinFET 12, respectively. Shallow trenchisolation (STI) regions 18 surround the bottom portions of the finstructures (or projections) 14 and 16 and prevent electricalinterference or crosstalk. The STI regions 18 are composed of siliconoxide. Alternatively, they could be silicon nitride, silicon oxynitride,other suitable materials, and/or combinations thereof. It is understoodthat although two fin structures are illustrated, additional parallelfins may be formed from substrate 13 in a similar manner.

The semiconductor device 10 also includes gate structures 20 and 22 thatoverlay a central portion of the fin structures (or projections) 14 and16, respectively. Gate structure 20 forms a part of NMOS FinFET 11 andgate structure 22 forms a part of PMOS FinFET 12. Further, gatestructures 20 and 22 each include a plurality of layers which will beexplained in more detail later. The gate structures 20 and 22 eachengage three surfaces of respective fin structures (or projections) 14and 16—the top surface and two adjacent side surfaces. The fin structure(or projection) 14 includes epitaxial silicon (Si) growths 24 on eachside of the gate structure 20. The epitaxial Si growths 24 are formed ona substrate protrusion 25. The substrate protrusion 25 is part of andextends from the substrate 13 and forms the core of the fin structure(or projection) 14. The gate structure 20 engages the central portion ofsubstrate protrusion 25 where the protrusion is free of the epitaxial Sigrowths 24. Fin structure (or projection) 16 includes epitaxial silicongermanium (SiGe) growths 26 on each side of the gate structure 22. Finstructure (or projection) 16 also includes a substrate protrusion (notvisible in FIG. 1), but only beneath the gate structure 22 and betweenthe epitaxial SiGe growths 26. Further, nickel silicide (NiSi) layers 28are disposed over the portions of the epitaxial Si growths 24 and theepitaxial SiGe growths 26 that extend above the STI regions 18.Alternatively, the silicide layers may be other types of silicide, forexample, titanium silicide. The fin structures (or projections) 14 and16 and gate structures 20 and 22 of semiconductor device 10 aresurrounded by an inter-level dielectric layer (ILD). But for the sake ofclarity, semiconductor device 10 is depicted in FIG. 1 without this ILD.

FIGS. 2-4 are diagrammatic fragmentary sectional views of thesemiconductor device 10 taken along lines 2-2, 3-3, and 4-4 in FIG. 1,respectively. FIG. 2 depicts a cross-section of the fin structure (orprojection) 14 and gate structure 20 that form portions of NMOS FinFET11. FIG. 3 depicts a cross-section of the fin structure (or projection)16 and gate structure 22 that form portions of PMOS FinFET 12. And dueto the non-linear path of line 4-4, FIG. 4 illustrates cross-sections ofboth the epitaxial growth 24 and the gate structure 20 of FinFET 11,even though these cross-sections do not lie in the same plane.

With reference to FIGS. 1 and 2, the fin structure (or projection) 14also includes a source region 30 and a drain region 32 that arerespectively defined on opposite sides of gate structure 20. The sourceand drain regions 30 and 32 each include portions of the epitaxial Sigrowths 24 that extend above the STI regions 18, and portions ofprotrusion 25. These source and drain regions are doped regions having adopant implanted therein that is appropriate for the design requirementsof the FinFET 11. Here, because fin structure (or projection) 14 is partof an NMOS device, source and drain regions 30 and 32 are doped with ann-type dopant such as phosphorus or arsenic, or combinations thereof.With reference to FIGS. 1 and 3, fin structure (or projection) 16includes a source region 34 and a drain region 36 that are respectivelydefined on opposite sides of gate structure 22. The source and drainregions 34 and 36 each include portions of the epitaxial SiGe growths 26that extend above the STI regions 18. Fin structure (or projection) 16is a portion of a PMOS device so source and drain regions 34 and 36 aredoped with a p-type dopant such as boron or BF2 or combinations thereof.

With reference again to FIGS. 1 and 2, fin structure (or projection) 14includes a strained channel region 38 defined in the portion of the finstructure (or projection) 14 surrounded on three sides by the gatestructure 20. The channel region 38 is interposed between the sourceregion 30 and the drain region 32 within the fin structure (orprojection) 14. Further, the channel region 38 is tensile-strained. Thatis, the crystal lattice of the silicon in the channel region isstretched, resulting in higher electron mobility during operation of theNMOS FinFET 11. In FIG. 2, a dashed arrow 39 diagrammatically denotesthe tensile strain imparted to channel region 38. A portion of thisstrain is induced by the epitaxial silicon growths 24 on either side ofchannel region 38. The epitaxial growths 24 have a lattice constantdifferent than that of the silicon in the channel region 38.Alternatively, the epitaxial growths 24 may be epitaxial silicon carbon(Si:C) instead of epitaxial silicon.

As noted above, the gate structure 20 includes a plurality of layersthat form the gate portion of the NMOS FinFET 11. In the lower-mostportion of gate structure 20, a dielectric layer 42 engages finstructure (or projection) 14 on three sides. Here, the dielectric layer42 is composed of a high-k dielectric material, such as hafnium oxide(HfOx). Alternatively, the dielectric layer 42 may include one or moreother high-k dielectrics such as hafnium silicon oxide (HfSiO) orhafnium silicon oxynitride (HfSiON) or may be composed of a materialwith a standard dielectric constant, such as silicon oxide. Thedielectric layer 42 has a thickness in a range from about 1 to about 200angstrom (Å). Although the dielectric layer 42 is illustrated as asingle layer in FIG. 2, it may optionally include additional layers suchas an interfacial layer of silicon oxide between the silicon of finstructure (or projection) 14 and the remainder of the dielectric layer42. A barrier layer 44 (also referred to as a capping layer, a diffusionlayer, or an etch stop layer) is disposed above the dielectric layer 42.The barrier layer 44 is composed of titanium nitride (TiN) having athickness in a range from about 5 to about 1000 Å. Alternatively, thebarrier layer 44 may include TaN or other materials suitable to reduceor eliminate the risk of Fermi level pinning between the high-k materialin dielectric layer 42 and adjacent polysilicon layers. A doped,conductive polysilicon layer 46 is disposed on the barrier layer 44. Thepolysilicon layer 46 has a thickness in a range of 50 to 200 Å.

The gate structure 20 further includes a conductive strain-inducinglayer 48. The strain-inducing layer 48 includes material that has athermal expansion coefficient larger than that of the polysilicon layer46 below it. Further, the crystal lattice constant of thestrain-inducing layer is different from that of the polysilicon layer46, resulting in lattice mismatch. The differences in the thermalexpansion coefficients and crystal lattice constants of strain-inducinglayer 48 and polysilicon material are such that the channel region 38below the gate structure 20 is tensile-strained after processing iscomplete. In the current embodiment, the strain-inducing layer 48 iscomposed of silicon germanium (SiGe) and has a thickness in a range ofabout 300 to 450 Å. In FIG. 2, a dashed arrow 50 diagrammaticallydenotes the strain-inducing characteristics of the SiGe layer 48.

The gate structure 20 includes a second doped, conductive polysiliconlayer 53 disposed above the strain-inducing layer 48. The polysiliconlayer 53 has a thickness of approximately 100 Å. A nickel silicide layer54 is disposed on the second polysilicon layer 53 and is the upper-mostlayer of the gate structure 20. As noted above, other types of silicidematerial may be used instead. Semiconductor device 10 also includessealing spacers 56 disposed on sidewalls of the gate structure 20. Thesealing spacers 56 are formed of silicon oxide but may optionallycontain silicon nitride as well or, alternatively, be composed of othersuitable dielectric material. The FinFET 11 further includes dummyspacers 58 disposed on the sealing spacers 56. The dummy spacers 58 areeach a multi-layer structure composed of both silicon nitride andsilicon oxide, but alternatively they may be integral structures.

With reference to FIGS. 3 and 4, and as noted above, FIG. 3 depicts across-section of the fin structure (or projection) 16 and gate structure22 that form portions of PMOS FinFET 12. And due to the non-linear pathof line 4-4, FIG. 4 illustrates cross-sections of both the epitaxialgrowth 26 and the gate structure 22 of FinFET 12. Fin structure (orprojection) 16 includes a strained channel region 59 defined in theportion of the fin structure (or projection) 16 surrounded on threesides by the gate structure 22. The channel region 59 is interposedbetween source region 34 and drain region 36 within the fin structure(or projection) 16. The channel region 59 is compression-strained. Thatis, the crystal lattice of the silicon in the channel region iscompressed , resulting in greater hole mobility. Greater hole mobilityin a PMOS transistor device lowers threshold voltage and increasesefficiency. Dashed arrows 60 diagrammatically indicate the compressivestrain in the channel region 59. As noted earlier in the description ofFIG. 1, fin structure (or projection) 16 includes epitaxial SiGe growths26. The epitaxial SiGe growths 26 have a larger crystal lattice constantthan the nearby silicon of the fin structure (or projection) 16. Thus,the epitaxial SiGe growths 26 cause the crystal lattice of the channelregion 59 disposed between the epitaxial SiGe growths 26 to becompressed, resulting in compressive channel strain. Dashed arrows 62diagrammatically indicate the strain-inducing character of the epitaxialSiGe growths.

The gate structure 22 overlays the fin structure (or projection) 16 andis disposed above and on the sides of the strained channel region 59defined therein. In the bottom portion of gate structure 22, adielectric layer 64 composed of a high-k dielectric material engages thechannel region 59. In the current embodiment, the dielectric layer 64 iscomposed of HfOx. Alternately, it could be formed of HfO2, HfSiO,HfSiON, HfTaO, HfTiO, HfZrO, AlO, ZrO, TiO, Ta2O5, Y2O3, SrTiO3 (STO),BaTiO3 (BTO), BaZrO, HfLaO, HfSiO, LaSiO, AlSiO, (Ba, Sr)TiO3 (BST),Al2O3, Si3N4, oxynitrides, other suitable high-k dielectric materials,and/or combinations thereof. Like dielectric layer 42 in gate structure20, dielectric layer 64 may optionally include an interfacial layer ofsilicon oxide or other oxide material between the channel region and theremainder of dielectric layer 64. A barrier layer 66 is disposed on thedielectric layer 64 and is similar to the barrier layer 44.

A U-shaped work function metal layer 68 is formed over the barrier layer66 in gate structure 22 and partially fills an opening 69. Because gatestructure 22 is a portion of a PMOS device, the work function metallayer 68 is composed of a p-type work function metal (P-metal), such astitanium nitride (TiN). Alternatively, the work function layer mayinclude other materials such as Ru, Mo, Al, WN, or combinations thereof.Further, the work function layer may alternatively be a multi-metallayer structure with a sufficiently high effective work function (EWF)value for proper PMOS device performance. For example, the work functionlayer may include both a TiN layer and a TaN layer. The gate structure22 contains a metal fill layer 70 that fills the portion of the opening69 not occupied by the work function layer 68. The metal fill layer 70is composed of a conductive metal, specifically aluminum (Al).Alternatively, the metal fill layer may include copper, tungsten,titanium, other suitable materials, and/or combinations thereof. TheFinFET 12 further includes, on sidewalls of the gate structure 22,sealer spacers 56 and dummy spacers 58 that are equivalent to thespacers 56 and 58 on gate structure 20.

FIGS. 5-12 are diagrammatic fragmentary sectional views similar to FIG.4 but showing the semiconductor device 10 during various successivestages of manufacture. The stages of manufacture depicted in FIGS. 5-12correspond with fabrication of the semiconductor device 10 using a CMOStechnology process flow. It should be understood that additionalprocesses may be provided before, during, and/or after the stagesillustrated in FIGS. 5-12, and that some selected processes may only bebriefly described if they are well known in the art.

Referring to FIG. 5, the silicon semiconductor substrate 13 is provided.The substrate protrusion 25 and a substrate protrusion 72 are formedfrom the substrate 13 using suitable processes includingphotolithography and etch processes. The photolithography processesinclude forming a photoresist layer (resist) overlying the substrate 13,exposing the resist to a pattern, performing post-exposure bakeprocesses, and developing the resist to form a masking element includingthe resist. The masking element is then used to etch recesses 74 intothe substrate 13, leaving the substrate protrusions 25 and 72. Therecesses forming substrate protrusions 25 and 72 may be etched usingreactive ion etch (RIE) and/or other suitable processes. Alternatively,the protrusions may be formed by double-patterning lithography (DPL)process. DPL allows for enhanced feature (e.g., fin) density. VariousDPL methodologies may be used, including double exposure (e.g., usingtwo mask sets), forming spacers adjacent features and removing thefeatures to provide a pattern of spacers, resist freezing, and/or othersuitable processes. After the substrate protrusions 25 and 72 areformed, silicon dioxide or other suitable dielectric is deposited andetched to form the shallow trench isolation (STI) regions 18 thatsurround and isolate the substrate protrusions. This may be accomplishedby any suitable process, which may include dry etching, wet etching, anda chemical vapor deposition process.

Next, a dielectric layer 80 with a thickness in the range of about 1 to200 Å is formed over the substrate protrusions 25 and 72 and the STIregions 18. The dielectric layer 80 is composed of a high-k dielectricmaterial, HfOx, and is deposited using chemical vapor deposition (CVD).The high-k material of dielectric layer 80 is deposited on all portionsof the protrusions 25 and 72 above the STI regions 18, including the topand side portions. Next, a barrier layer 82 of TiN is deposited by CVDover the dielectric layer 80 to a thickness in a range of about 5 to1000 Å. A polysilicon layer 84 is then formed by CVD over the barrierlayer 82. The polysilicon is deposited to a thickness in a range ofabout 50 to 200 Å. Next, a silicon germanium (SiGe) layer 86 with athickness in the range of about 300 to 450 Å is formed over thepolysilicon layer 84 using CVD. Finally, a second polysilicon layer 88is deposited to a thickness of about 100 Å over the SiGe layer 86 usingCVD. The layers 80, 82, 84, 86, and 88 may each alternatively be formedusing any other suitable process, such as physical vapor deposition(PVD), atomic layer deposition (ALD), high density plasma CVD (HDPCVD),metal organic CVD (MOCVD), remote plasma CVD (RPCVD), plasma enhancedCVD (PECVD), plating, other suitable methods, and/or combinationsthereof. Also, a photoresist layer 89 is deposited over the layer 88 andpatterned in a known manner to leave portions 89 that facilitate removalof portions of the layer stack in subsequent steps.

Referring now to FIG. 6, photolithography patterning processes areemployed to form the gate structure 20 and a temporary gate structure90, by removing the portions of the layers 80, 82, 84, 86, and 88 thatare not protected by the photoresist portions 89 (FIG. 5). Afterpatterning, the dielectric layer 42 (a portion of layer 80), the barrierlayer 44 (a portion of layer 82), the polysilicon layer 46 (a portion oflayer 84), the strain-inducing layer 48 (a portion of layer 86), and thepolysilicon layer 53 (a portion of layer 88) remain over substrateprotrusion 25, and form gate structure 20. And the dielectric layer 64(a portion of layer 80), the barrier layer 66 (a portion of layer 82), adummy polysilicon layer 92 (a portion of layer 84), a dummy SiGe layer94 (a portion of layer 86), and a second dummy polysilicon layer 96 (aportion of layer 88) remain over the substrate protrusion 72, and formtemporary gate structure 90. The photolithography patterning processused to form the gate structures may include any number of suitablesteps, such as photoresist coating (e.g., spin-on coating), soft baking,mask aligning, exposure, post-exposure baking, developing thephotoresist, rinsing, drying (e.g., hard baking), other suitableprocesses, and/or combinations thereof. Further, the photolithographyexposing process may be wholly replaced by other proper methods, such asmaskless photolithography, electron-beam writing, or ion-beam writing.The etching processes include dry etching, wet etching, and/or otheretching methods. It is understood that the above example does not limitthe processing techniques that may be utilized to form the layersdiscussed above.

After patterning the layers over the substrate protrusions 25 and 72,known processes are employed to form the sealing spacers 56 and dummyspacers 58 along the sides of the gate structure 20 and the temporarygate structure 90. After deposition and etching, the sealing spacers 56protect the four approximately vertical sides of each gate structure 20and 22. Next, a process is performed to etch two recesses 97 (FIGS. 3and 6) into substrate protrusion 72 (FIG. 5), one recess on each side oftemporary gate structure 90. As part of the process, a protection layer(not shown) is first formed to protect the substrate protrusion 25.Then, dry etching is used to etch away the exposed portions of substrateprotrusion 72. The recesses 97 may also be formed by wet etching or someother suitable process. A cleaning process may optionally be performedafter etching to clean the recesses 97 with hydrogen fluoride (HF) orother suitable solution.

Referring now to FIG. 7, the source and drain regions 30, 32, 34, and 36of the NMOS FinFET 11 and PMOS FinFET 12 are formed, of which two arevisible in FIG. 7. First, epitaxial silicon growths 24 are grown onsubstrate protrusion 25 on opposite sides of the gate structure 20. Theepitaxial growth processes include CVD deposition techniques (e.g.,vapor-phase epitaxy (VPE) and/or ultra-high vacuum CVD (UHV-CVD)),molecular beam epitaxy, and/or other suitable processes. The epitaxialprocess may further use gaseous and/or liquid precursors, which interactwith the composition of the substrate protrusion 25 (e.g., silicon). Thechannel region 38 (FIG. 2) is disposed between epitaxial growths 24 and,as the epitaxial Si is grown, tensile strain is induced in the channelregion due to lattice mismatch. Alternatively, epitaxial silicon carbon(Si:C) may be grown instead of epitaxial silicon. The protrusion 25 andnewly-formed epitaxial silicon growths 24 are then doped with n-typedopants, such as phosphorous or arsenic, to form the source and drainregions 30 and 32 of NMOS FinFET 11. Next, epitaxial growth processesare employed to form epitaxial silicon germanium growths 26 in therecesses 97 in substrate protrusion 72. The channel region 59 (FIG. 3)is disposed between the recesses 97 and, as the epitaxial SiGe is grownin the recesses 97, compression strain is induced in the channel regiondue to lattice mismatch. The epitaxial SiGe growths 26 are then dopedwith p-type dopants, such as boron, to form source and drain regions 34and 36 of PMOS FinFET 12. Optionally, other source and drain regions,such as lightly doped drain (LDD) and/or highly doped drain (HDD)regions, may be formed in the fin structures prior to forming the sourceand drain regions 30, 32, 34, and 36. Additionally, during this stage ofprocessing, hard mask layers 98 and 100 are formed on top of the gatestructure 20 and the temporary gate structure 90, respectively. The hardmask layers 98 and 100 are silicon nitride in the present embodiment butalternatively may be silicon oxynitride, silicon carbide, or othersuitable material.

Referring now to FIG. 8, semiconductor device 10 is subjected toprocessing to enhance the tensile strain in the channel region 38 of theNMOS FinFET 11. Specifically, stress memorization techniques (SMT) areperformed. First, a temporary capping layer 102 composed of siliconoxide and silicon nitride is deposited over the entire semiconductordevice 10, including the gate structures 20 and 90. A thickness of thesilicon oxide is in a range of about 50 Å to about 100 Å. A thickness ofthe silicon nitride is in a range of about 50 Å to about 250 Å. Next,semiconductor device 10 is subjected to a rapid thermal anneal (RTA) anda millisecond anneal (MSA). The RTA is performed at a peak temperatureof about 990 to 1010° C., at a pressure of about 760 torr, and for aduration in a range of about 1 to 4 seconds. The MSA is performed at apeak temperature of about 1250° C., at a pressure of about 760 ton, andfor a duration in a range of about 0.4 to 0.8 milliseconds. The SMTprocess creates tensile strain in the channel region 38 by “freezing”the temperature-related stress condition of the gate structure 20created during the RTA and MSA. Namely, the larger coefficient ofthermal expansion of the strain-inducing SiGe layer 48 forces thecrystal lattice of the polysilicon layer 46 below it to abnormallyexpand during the RTA and MSA. Then, during recrystallization of thepolysilicon crystal lattice after the high-temperature anneals, thepolysilicon layer 46 retains or “memorizes” the tensile strain conditioninduced during the anneals. This tensile strain is propagated downthrough the gate structure 20 and into the channel region 38. After theSMT process, the temporary capping layer 102 is removed and processingcontinues.

With reference now to FIG. 9, a silicidation process is performed onsemiconductor device 10. First, the hard mask layer 98 is removed fromthe gate structure 20 to expose the polysilicon layer 53, while leavinghard mask layer 100 in place. Next, a silicidation process such as aself-aligned silicide (salicide) process is performed to grow a silicidelayer on any exposed silicon-based surface. Specifically, a metalmaterial such as nickel is deposited over FinFETs 11 and 12, thetemperature is raised to cause a reaction between the nickel and anysilicon exposed to the nickel, and then the un-reacted nickel is etchedaway. During silicidation, nickel silicide layers 28 are formed on theepitaxial Si growths 24 and epitaxial SiGe growths 26, and silicidelayer 54 is formed over the polysilicon layer 53 in the gate structure20. Hard mask layer 100 remains on temporary gate structure 90 duringsilicidation to prevent the formation of silicide on dummy polysiliconlayer 96, but is removed after silicidation. After the silicideformation on the epitaxial growths, the fin structures (or projections)14 and 16 are complete.

Referring now to FIG. 10, an interlayer (or inter-level) dielectric(ILD) layer 104 is next formed over the semiconductor device 10,including gate structures 20 and 90 and fin structures (or projections)14 and 16. The ILD layer 104 is composed of a dielectric such as siliconoxide. Subsequent to the deposition of the ILD layer 104, a chemicalmechanical polishing (CMP) process is performed, until a top portion ofeach gate structure 20 and 90 is exposed. Next, a patterned photoresistlayer 106 is deposited over a portion of the semiconductor device 10 toprotect the gate structure 20.

Referring now to FIGS. 11 and 12, a gate replacement process isperformed, wherein the top three layers of the temporary gate structure90 are removed and replaced with a metal gate electrode. In particular,FIG. 11 illustrates the temporary gate structure 90 after removal of thedummy polysilicon layers 92 and 96 and the dummy SiGe layer 94. Thephotoresist layer 106 protects the gate structure 20 during this removalof the dummy layers. The dummy layers may be removed from the temporarygate structure 90 simultaneously or independently by any suitableprocess, such as a dry etching and/or wet etching process. After etchingaway the layers 92, 94, and 96, the top surface of barrier layer 66 andthe inner surfaces of sealing spacers 56 respectively define bottom andside surfaces of the opening 69. Next, as shown in FIG. 12, photoresistlayer 106 is removed and the opening 69 is filled with a metal gateelectrode that includes work function layer 68 and metal fill layer 70,to thereby form the final gate structure 22. Specifically, filling theopening 69 includes then depositing the work function layer 68 over thebarrier layer 42 and on the sides of the sealing spacers 56 anddepositing the metal fill layer 70 in the remainder of the opening 69.In the present embodiment, the work function layer 68 is formed by thedeposition of p-type work function metal (P-metal) such as TiN to athickness in a range of about 10 Å to 200 Å. And the metal fill layer 70is formed by the deposition of aluminum or other conductive metal suchas copper, tungsten, or titanium. Alternatively, the opening 69 may befilled with only the metal fill layer 70, and the gate structure 22 maybe tuned to have an appropriate work function value in other known ways.Subsequent to the formation of the gate structure 22, a CMP process isperformed to planarize the top portions of the gate structures 20 and 22and the ILD layer 104.

It is understood that the semiconductor device 10 will undergo furtherprocessing to complete fabrication. For example, a not-illustratedmultilayer interconnection (MLI) including metal layers (e.g., M1, M2,etc.) and inter-metal dielectric (IMD) will be formed above fin and gatestructures 14, 16, 20, and 22 in order to electrically couple variousdevice parts to form an integrated circuit. The multilayerinterconnection includes vertical interconnects, such as conventionalvias or contacts, and horizontal interconnects, such as metal lines. Thevarious interconnection features may utilize various conductivematerials including copper, tungsten and silicide. In one example, adamascene process is used to form copper multilayer interconnectionstructure.

FIG. 13 is a high-level flowchart showing the process 120 that wasdescribed above in association with FIGS. 5-12. Process 120 begins atblock 122 where the substrate protrusions 25 and 72 are formed from thesubstrate 13. The STI regions 18 are also formed after the protrusionsare formed. The process 120 proceeds to block 124 where the dielectriclayer 80, the barrier layer 82, the polysilicon layer 84, the silicongermanium layer, 86 and the second polysilicon layer 88 are formed overthe substrate protrusions 25 and 72. Then, in block 126, the layersformed in block 124 are patterned into the gate structure 20 and thetemporary gate structure 90. The gate structure 20 overlays the channelregion 38 of the fin structure (or projection) 14 and the temporary gatestructure 90 overlays the channel region 59 of the fin structure (orprojection) 16. Process 120 proceeds to block 128 where the epitaxial Sigrowths 24 are grown on the substrate protrusion 25 on each side of thegate structure 20. And the epitaxial SiGe growths 26 are grown on thesubstrate protrusion 72 on each side of the gate structure 90.Additionally, the epitaxial Si growths 24 and substrate protrusion 25are doped with n-type dopants to form the source and drain regions 30and 32. And the epitaxial SiGe growths 26 are doped with p-type dopantsto form the source and drain regions 34 and 36. Also, hard mask layers98 and 100 are formed on the top of gate structures 20 and 90. Then, inblock 130, the temporary capping layer 102 is deposited over thesemiconductor device 10. Subsequently, a RTA and MSA are performed toinduce tensile channel strain in the channel region 38, and the cappinglayer is removed. Next, in block 132, the silicide layer 54 is formedover the gate structure 20 and the silicide layers 28 are formed on theepitaxial growths. A gate replacement process is then performed over thecourse of blocks 134 and 136. Specifically, in block 134, the dummypolysilicon layers 92 and 96 and the dummy SiGe layer 94 are removedfrom the temporary gate structure 90, which creates the opening 69 abovethe barrier layer 66. Next, in block 136, the opening 69 is filled withthe work function layer 68 and metal fill layer 70 to form the finalgate structure 22.

The semiconductor device 10 is not limited to the aspects and structureof the integrated circuit described above. For example, a singleintegral gate structure might overlay both of the fin structures (orprojections) 14 and 16 and serve as the gate structure of both the NMOSFinFET 11 and the PMOS FinFET 12. In such a case, during the gatereplacement process described in association with FIGS. 11 and 12, theportion of the integral gate structure overlaying fin structure (orprojection) 14 would be protected while the portion overlaying finstructure (or projection) 16 would be replaced with a metal gateelectrode. Further, the integrated circuit in the semiconductor device10 can also include passive components such as resistors, capacitors,inductors, and/or fuses; and active components, such as MOSFETsincluding p-channel MOSFETs (pMOS transistors) and n-channel MOSFETs(nMOS transistors), complementary metal-oxide-semiconductor transistors(CMOSs), high voltage transistors, and/or high frequency transistors;other suitable components; and/or combinations thereof.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduce herein. Thoseskilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

1. An apparatus comprising: a substrate having a strained channel regiontherein; a dielectric layer disposed at least partly over the channelregion; a first conductive layer disposed over the dielectric layer, andhaving a characteristic with a first value; a strain-inducing conductivelayer disposed over the first conductive layer, and having thecharacteristic with a second value, wherein the second value isdifferent from the first value; and a second conductive layer disposedover the strain-inducing conductive layer, and having the characteristicwith the first value.
 2. An apparatus according to claim 1, wherein thecharacteristic is one of a thermal expansion coefficient and a crystallattice constant.
 3. An apparatus according to claim 2, wherein thecharacteristic is the crystal lattice constant; and wherein the firstand second conductive layers both have a first thermal expansioncoefficient and the strain-inducing conductive layer has a secondthermal expansion coefficient different from the first thermal expansioncoefficient.
 4. An apparatus according to claim 3, wherein the first andsecond conductive layers are doped polysilicon and the strain-inducingconductive layer is silicon germanium (SiGe).
 5. An apparatus accordingto claim 1, wherein the substrate includes an upwardly-extendingprojection, the channel region being at least partly in the projection;and including a gate structure that includes the dielectric layer, thefirst and second conductive layers, and the strain-inducing conductivelayer, the gate structure engaging the projection adjacent to thechannel region.
 6. An apparatus according to claim 5, wherein the firstand second conductive layers are doped polysilicon and thestrain-inducing conductive layer is silicon germanium (SiGe).
 7. Anapparatus according to claim 6, wherein the strain-inducing conductivelayer has a thickness in a range of approximately 300 to 450 angstromsand the first and second conductive layers each have a thickness in arange of approximately 50 to 200 angstroms.
 8. An apparatus according toclaim 1, wherein the strain in the channel region is tensile strain. 9.An apparatus comprising: a substrate; first and second projectionsextending upwardly from the substrate, the first projection having atensile-strained first channel region therein and the second projectionhaving a compression-strained second channel region therein; and firstand second gate structures engaging the first and second projectionsadjacent to the first and second channel regions, respectively; whereinthe first gate structure includes: a dielectric layer adjacent the firstchannel region; a first conductive layer disposed over the dielectriclayer; a strain-inducing conductive layer disposed over the firstconductive layer; and a second conductive layer disposed over thestrain-inducing conductive layer; and wherein the second gate structureincludes: a high-k dielectric layer adjacent the second channel region;and a metal layer disposed over the high-k dielectric layer.
 10. Anapparatus according to claim 9, wherein the first and second conductivelayers are doped polysilicon and each have a first thermal expansioncoefficient and a first crystal lattice constant; and wherein thestrain-inducing conductive layer has a second thermal expansioncoefficient different from the first thermal expansion coefficient, anda second crystal lattice constant different from the first crystallattice constant.
 11. An apparatus according to claim 10, wherein thestrain-inducing conductive layer is silicon germanium (SiGe).
 12. Anapparatus according to claim 11, wherein the strain-inducing conductivelayer has a thickness in a range of approximately 300 to 450 angstromsand the first and second conductive layers each have a thickness in arange of approximately 50 to 200 angstroms.
 13. An apparatus accordingto claim 9, including: first epitaxial growths on portions of the firstprojection at each side of the first gate structure, the first epitaxialgrowths imparting tensile strain to the first channel region; and secondepitaxial growths on portions of the second projection at each side ofthe second gate structure, the second epitaxial growths impartingcompressive strain to the second channel region.
 14. An apparatusaccording to claim 13, wherein the first epitaxial growths are epitaxialsilicon and the second epitaxial growths are epitaxial silicon germanium(SiGe).
 15. An apparatus according to claim 9, wherein the second gatestructure includes a work function layer disposed between the high-kdielectric layer and the metal layer.
 16. A method comprising: providinga substrate; forming a projection extending upwardly from the substrate,the projection having a channel region therein; forming a gate structureengaging the projection adjacent to the channel region, the gatestructure having spaced first and second conductive layers and astrain-inducing conductive layer disposed between the first and secondconductive layers; forming a capping layer over the gate structure;imparting strain to the channel region, including performing a heattreatment on the gate structure; and removing the capping layer.
 17. Amethod according to claim 16, wherein the imparting strain is carriedout in a manner that imparts tensile strain to the channel region; andwherein the performing the heat treatment includes performing a rapidthermal anneal and a millisecond anneal.
 18. A method according to claim17, wherein the performing the rapid thermal anneal is carried out at atemperature between approximately 990 and 1010° C.; and wherein theperforming the millisecond anneal is carried out at a temperature ofapproximately 1250° C.
 19. A method according to claim 16, wherein theforming the gate structure includes: forming a dielectric layer; formingthe first conductive layer out of doped polysilicon and over thedielectric layer; forming the strain-inducing layer out of silicongermanium and over the first conductive layer; and forming the secondconductive layer out of doped polysilicon and over the strain-inducingconductive layer.
 20. A method according to claim 19, wherein theprojection is a first projection, the channel region is a first channelregion, and the gate structure is a first gate structure; and including:forming a second projection extending upwardly from the substrate, thesecond projection having a second channel region therein; forming asecond gate structure engaging the second projection adjacent to thesecond channel region, the second gate structure having a dummyelectrode; forming an inter-level dielectric (ILD) over the substrate,projections, and gate structures after the removing the capping layer;performing a polishing on the ILD to expose upper ends of both gatestructures; forming a protection layer to protect the first gatestructure; removing the dummy electrode from the second gate structurethereby forming an opening; removing the protection layer; anddepositing metal in the opening in the second gate structure.